1. Field of the Invention
The present invention relates to a holder for a drive piston of a setting tool.
2. Description of the Prior Art
European Publication EP-O 346275 B1 discloses an explosive powder charge-operated setting tool including a piston guide and a drive piston displaceable in the piston guide. In the setting tool, there are provided braking balls for engaging the drive piston and a spring for biasing the braking balls into engagement with the drive piston. The spring is formed as a ring spring for generating a biasing force acting in a radial, with respect to the axial extent of the drive piston direction, on the braking balls. The ring spring is provided on its inner profile with a bearing surface acting on the braking ball. The bearing surface is inclined to the piston at an acute angle that opens in a direction opposite a setting direction. When the driving piston moves in the setting direction, it entrains the braking balls therewith. The braking balls expand the ring spring, which results in the bearing surface transmitting the radial biasing force to the braking balls and, thereby, to the drive piston.
In the ignition-ready position of the drive piston, the braking balls engage, under the biasing force of the ring spring, the body of the drive piston. Upon displacement of the drive piston, as a result of the firing of the setting tool, in the drive-out or setting direction, the drive piston, at the start of its movement, entrains the braking balls with it, rolling them over. As discussed, the braking balls expand the ring spring, and the bearing surface applies to the braking balls a radial biasing force of the ring spring, which is divided in components acting in direction opposite to the setting direction and radially, with respect to the drive piston. The radially displaced, under the action of the biasing force, braking balls are pressed against the piston body, braking the same. Even after a short displacement of the drive piston rearwardly, the braking effect can be lifted, with the braking balls rolling back, releasing the tensioning of the spring. Upon release of the ring spring, it does not bias the balls anymore toward the drive piston. Further, a possibility still remains that the drive piston would be displaced, before ignition or firing of the setting tool, in the setting direction as a result of, e.g., the setting tool being pressed hard against a constructional component. In this case, the displacement of the drive piston in the return direction is effected due to cooperation of the ring spring with the braking balls.
U.S. Pat. No. 4,162,033 discloses a setting tool with a braking device that continuously applies a braking force to the drive piston.
An object of the present invention is to provide a piston holder having a simplified design and which would reliably retain the drive piston in its ignition-ready position in the absence of ignition.
This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a piston holder for a drive piston of a setting tool and including at least one friction member for applying pressure to a circumferential surface of the drive piston and having an adjusting surface remote from the drive piston and rising toward a rear, in a setting direction of the setting tool, end of the drive piston, and a pressure element stationary with respect to an axial direction of the drive piston and which is always in a pressure contact with the adjusting surface.
The pressure element insures that the friction member is in a constant contact with the drive piston. The friction member is primarily located in the region of the drive piston body. However, the friction member can be positioned somewhere else with respect to the circumferential surface of the drive piston. When the drive piston, upon actuation of the setting tool, is displaced in the setting direction, it entrains therewith the friction member. As a result, the inclined, in the setting direction adjusting surface is pressed more strongly against the pressure element, whereby the friction between the friction member and the drive piston increases. However, this friction is overcome when the setting tool driving energy reaches its maximum, and the drive piston is able to drive in a fastening element, e.g., in a constructional component or any other object. When the drive piston returns to its initial position, it again entrains the friction member therewith. However, in this case, due to inclination of the adjusting surface in the direction opposite to the direction of movement of the drive piston, the pressure acting between the pressure element and the friction member is reduced significantly, so that during the return movement of the drive piston, the friction between the friction member and the drive piston is reduced practically to a minimum. Still, some friction between the friction member and the drive piston remains, so that the latter can be reliably held in its ignition-ready position. This is insured by a constant contact of the friction with the pressure element.
According to the present invention, the friction member can extend only over a portion of the circumference of the drive piston and be formed as a wedge or a cone, with the adjusting surface being formed as a wedge or conical surface. During the movement of the drive piston in the setting direction or back to its ignition-ready position, the pressure element will run up or down, respectively, over the adjusting surface, providing for the above-described friction action between the friction member and the drive piston. For increasing the friction effect, several friction members and associated therewith, pressure elements can be arranged along the drive piston circumference at a substantially same angular distance therebetween.
The friction member can be formed as a rigid body, with a non-rigid arrangement of the pressure element. Also as a friction member, a wedge or conical body can be used. In this case, the pressure element can be formed as a leaf spring, compression spring, elastomeric spring, or as a ring spring. When the pressure element is formed as a ring spring. When the pressure element is formed as a ring spring, it can apply pressure to several friction members. Pressure contact members can be provided between the above-mentioned pressure elements and the friction members in order to reduce friction between the pressure element and the adjusting surface of the friction member. As a pressure contact member, e.g., a bolt, which extends in a tangential, with respect to the drive piston, direction, can be used. The bolt can be supported sidably or rotatably. When a bolt is used, it will be displaced upwardly and downwardly with the displacement of the drive piston in the setting and opposite directions, respectively, to provide for the desired friction action between the friction member and the drive piston.
According to another embodiment of the present invention, the adjusting surface of the friction member can be formed non-rigid, with stationary or fixed positioning of the pressure element. Thus, e.g., the friction member can be formed of an elastic material or be connected with a suitably inclined, elastic adjusting surface. In this case, the pressure element can have only, e.g., a radially stationary positioned bolt extending tangentially with respect to the drive piston.
In accordance with a still further embodiment of the present invention, the friction member can be formed as a conical spring sleeve, with the pressure element having an inner cone for receiving the spring sleeve. The conical spring sleeve, which is always in a pressure contact with the inner cone, will be pressed against the inner cone more or less strongly, dependent on whether the drive piston moves, respectively, in the setting or opposite direction, with an accompanying increase or decrease of friction between the spring sleeve and the drive piston. In this case also, the previously described change of the friction force action between the friction member and the drive piston would be retained, with the drive piston being reliably held in its ignition-ready position.
The conical spring sleeve can be provided with axial slots in order to obtain a better effect, or be formed of several sections.
In addition, the conical spring sleeve can be bent downwardly at its narrow end, or be provided at this end with a meander shape to form an elastic pressure region that would apply permanently pressure to the drive piston in the radial direction. This insures a minimal friction between the spring sleeve and the drive piston. In this case also, axial slots can be formed in the spring sleeve to improve elasticity in the sleeve pressure region.
In order to retain a contact between the friction member and the pressure element, according to a further development of the present invention, there is provided a spring element for biasing the friction member in the axial direction. This spring element insures further reduction of friction between the friction member and the drive piston. The spring element is designed for insuring a constant contact between the friction member and the pressure element when the drive piston entrains the friction member during its movement to its initial, ignition-ready position.
To this end, the movement of the friction member in the direction toward the rear end of the drive piston can be limited by a stop. In this case, the axially acting spring element can be dispensed with.
The novel features of the present invention which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to is construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiments, when read with reference to the accompanying drawings.